Multi-output dc-to-dc conversion apparatus with voltage-stabilizing function

ABSTRACT

A multi-output DC-to-DC conversion apparatus with a voltage-stabilizing function includes a center-tapped main transformer, a semiconductor component group, and a triggering controller. The DC-to-DC conversion apparatus provides at least two output voltages which are a main output voltage and an auxiliary output voltage, respectively. The auxiliary output voltage is functioned as an input voltage of a buck converter; and, as a result, the auxiliary output voltage can be adjusted to obtain a lower variable DC voltage. The triggering controller is used to stabilize the main output voltage and the auxiliary output voltage. Therefore, the main transformer provides one or two secondary windings to step down the auxiliary output voltage so as to increase efficiency of the buck converter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 12/824,871 filed on Jun. 28, 2010. The entire disclosure isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a DC-to-DC conversion apparatus, andmore particularly to a multi-output DC-to-DC conversion apparatus with avoltage-stabilizing function.

2. Description of Prior Art

For a variety of electronic products, providing the most suitable DCvoltage level for themselves has become a necessary trend. Thus, auseful method of converting the standard supply voltage into a requiredvoltage for load is necessary, and which should satisfy general-purpose,high-efficiency, and high-reliability requirements. Because mostelectronic products, such as televisions, audios, computers, aresupplied with DC-voltage electricity, the utility-line AC voltage has tobe converted into DC voltages of various levels to make the electronicproducts perform properly.

Reference is made to FIG. 1 which is an architecture block diagram of aprior art power supply. The power supply mainly includes an EMI filter10A, a rectifier 20A, a power factor corrector 30A, a DC-to-DC converter40A, and a buck converter 70A. The DC-to-DC converter 40A has aplurality of power switches (not shown) and a main transformer (notshown). The EMI filter 10A is electrically connected to an AC source Vsto eliminate the conducted EMI noises in the AC lines. Therefore, incase of possible interference for different apparatuses connected to thepower supply in the same distribution system could be restrained. Therectifier 20A is electrically connected to the EMI filter 10A to convertAC supply outputted form the EMI filter 10A to DC supply. The powerfactor corrector 30A is electrically connected to the rectifier 20A toimprove the power factor of the power supply. The DC-to-DC converter 40Ais electrically connected to the power factor corrector 30A to provide avoltage for the main transformer by controlling the power switchesthough a PWM control scheme. Therefore, the outputted DC supply of thepower factor corrector 30A can be provided from the primary winding ofthe main transformer to the secondary winding thereof for energyconversion. The buck converter 70A is electrically connected to anoutput terminal Vo1 of the DC-to-DC converter 40A to provide a lower DCvoltage.

The most popular power supplies provide +12V, +5Vsb, +5V, and +3.3Voutput voltages, which are supplied to desktop computers. Forhigh-efficiency applications, the +12V output voltage (labeled as Vo1 inFIG. 1) is converted from the main transformer; whereas, the +5V outputvoltage (labeled as Vb1) and the +3.3V output voltage (labeled as Vb2)are obtained by converting the +12V voltage by the buck converter 70A.More particularly, the +12V voltage is more than two times as higher asthe +5V (and even more than three times as higher as the +3.3V).Accordingly, a large voltage difference between the input voltage andthe output voltage of the buck converter 70A would increase core lossesof the internal magnetic components and switching losses of the powerswitches. Therefore, the efficiency of the buck converter 70A isreduced, particularly in much higher frequency operations.

Accordingly, it is desirable to provide, a multi-output DC-to-DCconversion apparatus with a voltage-stabilizing function to providelower-level voltage functioned as an input voltage to the buckconverter, thus increasing efficiency of the buck converter.

SUMMARY OF THE INVENTION

In order to solve above-mentioned problems, a multi-output DC-to-DCconversion apparatus with a voltage-stabilizing function is disclosed.The multi-output DC-to-DC conversion apparatus generates a main outputvoltage and an auxiliary output voltage. The auxiliary output voltage islower than the main output voltage and is functioned as an input voltageof a buck converter, and the buck converter is provided to convert theauxiliary output voltage into at least one lower adjustable DC voltage.The multi-output DC-to-DC conversion apparatus includes a maintransformer, a semiconductor component group, and a triggeringcontroller.

The main transformer has a primary winding and a secondary winding, andthe secondary winding has a dotted terminal, a non-dotted terminal, anda medium terminal. The semiconductor component group is electricallyconnected to the dotted terminal and the non-dotted terminal of thesecondary winding of the main transformer. One output terminal of thesemiconductor component group is the ground, and the other outputterminal is a main output terminal, which provides the main outputvoltage to the ground. The medium terminal is an auxiliary outputterminal, which provides the auxiliary output voltage to the ground.

The triggering controller is electrically connected to the main outputterminal and the auxiliary output terminal and generates a plurality ofcontrol signals to control switching frequency of the semiconductorcomponent group for stabilizing the main output voltage and theauxiliary output voltage.

Therefore, a center-tapped of the main transformer with the secondarywinding provides a lower-level voltage, which is functioned as the inputvoltage of the buck converter to increase efficiency of the buckconverter.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary, and are intended toprovide further explanation of the invention as claimed. Otheradvantages and features of the invention will be apparent from thefollowing description, drawings and claims.

BRIEF DESCRIPTION OF DRAWING

The features of the invention believed to be novel are set forth withparticularity in the appended claims. The invention itself, however, maybe best understood by reference to the following detailed description ofthe invention, which describes an exemplary embodiment of the invention,taken in conjunction with the accompanying drawings, in which:

FIG. 1 is an architecture block diagram of a prior art power supply;

FIG. 2 is an architecture block diagram of a power supply according tothe present invention;

FIG. 3A is a circuit diagram of a first embodiment of a multi-outputDC-to-DC conversion apparatus with a voltage-stabilizing functionaccording to the present invention;

FIG. 3B is a circuit diagram of the first embodiment that themulti-output DC-to-DC conversion apparatus is operated with current in apositive half-cycle;

FIG. 3C is a circuit diagram of the first embodiment that themulti-output DC-to-DC conversion apparatus is operated with current in anegative half-cycle;

FIG. 4A is a circuit diagram of a second embodiment of a multi-outputDC-to-DC conversion apparatus with a voltage-stabilizing function;

FIG. 4B is a circuit diagram of the second embodiment that themulti-output DC-to-DC conversion apparatus is operated with current in apositive half-cycle; and

FIG. 4C is a circuit diagram of the second embodiment that themulti-output DC-to-DC conversion apparatus is operated with current in anegative half-cycle.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made to the drawing figures to describe thepresent invention in detail.

Reference is made to FIG. 2 which is an architecture block diagram of apower supply according to the present invention. Parts of elements inthe power supply are similar to those in the above-mentioned prior artpower supply. The power supply includes an EMI filter 10, a rectifier20, a power factor corrector (PFC) 30, a DC-to-DC conversion apparatus60, and a buck converter 70. The DC-to-DC conversion apparatus 60 has aplurality of power switches (not shown), a main transformer 500, asemiconductor component group 600, and a triggering controller 606. Theamount of the power switches required depends on the topology of theDC-to-DC conversion apparatus 60. The electrical connection andfunctions of the units in the power supply are similar to those in theprior art power supply, thus, the detail description is omitted here forconciseness. However, one major difference between the prior art powersupply and the present power supply is that the main transformer 500 isa center-tapped transformer. More particularly, different arrangementsof the secondary-side winding of the center-tapped transformer 500provide various embodiments for the multi-output DC-to-DC conversionapparatus. The detailed description will be made as follows.

Reference is made to FIG. 3A which is a circuit diagram of a firstembodiment of a multi-output DC-to-DC conversion apparatus with avoltage-stabilizing function according to the present invention. Themulti-output DC-to-DC conversion apparatus 60 generates at least twooutput voltages, namely, a main output voltage and an auxiliary outputvoltage. The auxiliary output voltage is lower than the main outputvoltage and is functioned as an input voltage of a buck converter, andthe buck converter is provided to convert the auxiliary output voltageinto at least one lower adjustable DC voltage. The multi-output DC-to-DCconversion apparatus 60 includes a main transformer 500, a semiconductorcomponent group 600, and a triggering controller 606.

The main transformer 500 has a primary winding (not labeled) and asecondary winding (not labeled). The primary winding has a dottedterminal (not labeled) and a non-dotted terminal (not labeled). Thesecondary winding has a center tap, a dotted terminal (not labeled), anon-dotted terminal (not labeled), and a medium terminal (not labeled).

The semiconductor component group 600 is electrically connected betweenthe dotted terminal and the non-dotted terminal of the main transformer500. One output terminal of the semiconductor component group 600 is theground (not labeled) and the other output terminal is a main outputterminal Vo1, and the main output terminal Vo1 provides the main outputvoltage to the ground. The medium terminal is an auxiliary outputterminal Vo2, which provides the auxiliary output voltage to the ground.

The semiconductor component group 600 is composed of four semiconductorcomponents, which have a first semiconductor component 601, a secondsemiconductor component 602, a third semiconductor component 603, and afourth semiconductor component 604, respectively. Each of the foursemiconductor components 601-604 has at least one first terminal (notlabeled) and a second terminal (not labeled). As shown in FIG. 3A, thedotted terminal of the secondary winding of the main transformer 500 iselectrically connected to the second terminal of the first semiconductorcomponent 601, and the non-dotted terminal of the secondary winding iselectrically connected to the first terminal of the fourth semiconductorcomponent 604.

All of the four semiconductor components 601-604 are controllablesemiconductor components, such as MOSFETs, BJTs, or IGBTs. In thisexample, more particularly, the MOSFETs are exemplified for furtherdemonstration.

In addition, the second terminal of the first semiconductor component601 is electrically connected to the first terminal of the thirdsemiconductor component 603 in series. The second terminal of the secondsemiconductor component 602 is electrically connected to the firstterminal of the fourth semiconductor component 604 in series. The firstterminal of the first semiconductor component 601 is electricallyconnected to the first terminal of the second semiconductor component602 to form the main output voltage of the semiconductor component group600. Also, the second terminal of the third semiconductor component 603is electrically connected to the second terminal of the fourthsemiconductor component 604 to form the ground.

The triggering controller 606 is electrically connected to the mainoutput terminal Vo1 and the auxiliary output terminal Vo2 to generate aplurality of control signals S1-S4. The duty cycle of the semiconductorcomponent group 600 is controlled by the control signals S1-S4 tostabilize the main output voltage and the auxiliary output voltage. Thedetailed operation of the triggering controller 606 will be madehereinafter.

Reference is made to FIG. 3B which is a circuit diagram of the firstembodiment that the multi-output DC-to-DC conversion apparatus isoperated with current in a positive half-cycle. The main transformer 500receives a processed primary-side current from the front-end circuit,and the primary-side current is a quasi-sinusoidal current. Thus, theprimary-side current hereinafter is referred to as the quasi-sinusoidalcurrent. During the positive half cycle of the quasi-sinusoidal current,the quasi-sinusoidal current flows into the dotted terminal of theprimary winding; and a secondary-side current flows out the non-dottedterminal of the secondary winding. In this condition, the firstsemiconductor component 601 and the fourth semiconductor component 604of the semiconductor component group 600 are forward biased, whereas thesecond semiconductor component 602 and the third semiconductor component603 are reverse biased. Hence, the first semiconductor component 601 andthe fourth semiconductor component 604 are turned-on; the secondsemiconductor component 602 and the third semiconductor component 603are turned-off. The direction of arrow, shown in FIG. 3B, represents thedirection of current flowing in the main transformer 500 and thesemiconductor component group 600. Besides, the DC-to-DC conversionapparatus 60 further have inductor-capacitor filters (not labeled),which are used to filter the main output voltage and the auxiliaryoutput voltage.

Reference is made to FIG. 3C which is a circuit diagram of the firstembodiment that the multi-output DC-to-DC conversion apparatus isoperated with current in a negative half-cycle. During the negative halfcycle of the quasi-sinusoidal current, the quasi-sinusoidal currentflows out the dotted terminal of the primary winding; and thesecondary-side current flows into the dotted terminal of the secondarywinding. In this condition, the second semiconductor component 602 andthe third semiconductor component 603 of the semiconductor componentgroup 600 are forward biased, whereas the first semiconductor component601 and the fourth semiconductor component 604 are reverse biased.Hence, the second semiconductor component 602 and the thirdsemiconductor component 603 are turned-on; the first semiconductorcomponent 601 and the fourth semiconductor component 604 are turned-off.The direction of arrow, shown in FIG. 3C, represents the direction ofcurrent flowing in the main transformer 500 and the semiconductorcomponent group 600. Besides, the DC-to-DC conversion apparatus 60further have inductor-capacitor filters (not labeled), which are used tofilter the main output voltage and the auxiliary output voltage.

Accordingly, the center-tapped main transformer 500 with the singlesecondary winding is applied to provide two output voltages from theDC-to-DC conversion apparatus 60:

1. The main output voltage is generated from the entire secondarywinding;

2. The auxiliary output voltage is generated from the medium terminal ofthe secondary winding.

However, the two-output DC-to-DC conversion apparatus 60 is example fordemonstration and not for limitation of the present invention.

Evidently, the main output voltage is twice of the auxiliary outputvoltage. More particularly, the main output voltage and the auxiliaryoutput voltage can be stabilized in the predetermined voltages by thevoltage-stabilizing feedback control.

In order to stabilize the main output voltage and the auxiliary outputvoltage in the predetermined voltages to supply the loads due to thevariation of the input voltage as well as the load variation. Thefollowing schemes can be employed:

A comparator (not shown) is used to compare the main output voltage witha first reference voltage (not shown). The first reference voltage is,namely, the expected main output voltage of the multi-output DC-to-DCconversion apparatus 60, and which is assumed as +12V. Moreparticularly, a voltage difference between the actual main outputvoltage and the first reference voltage is fed back to the triggeringcontroller 606, which can be a PWM controller in this embodiment. Whenthe main output voltage is higher than the first reference voltage, thecomparator outputs a low-level signal to increase switching frequency ofthe first control signal S1 and the fourth control signal S4 during thepositive half cycle of the quasi-sinusoidal current. Where the firstcontrol signal S1 and the fourth control signal S4 are a driving signalfor a gate-source voltage Vgs of the first semiconductor component 601and that of the fourth semiconductor component 604, respectively. Inaddition, the main output voltage would increase when the DC-to-DCconversion apparatus 60 operates at a light-load condition. Thus, duringthe negative half cycle of the quasi-sinusoidal current, the comparatoroutputs a low-level signal to increase switching frequency of the secondcontrol signal S2 and the third control signal S3, thus reducing themain output voltage and stabilizing it at +12V. Where the second controlsignal S2 and the third control signal S3 are a driving signal for agate-source voltage Vgs of the second semiconductor component 602 andthat of the third semiconductor component 603, respectively. Inaddition, because the auxiliary output voltage is proportional to themain output voltage (in this example, the main output voltage is twiceof the auxiliary output voltage), the auxiliary output voltage can bestabilized at +6V.

Similarly, a comparator (not shown) is used to compare the auxiliaryoutput voltage with a second reference voltage (not shown). The secondreference voltage is, namely, the expected auxiliary output voltage ofthe multi-output DC-to-DC conversion apparatus 60, and which is assumedas +6V. More particularly, a voltage difference between the actualauxiliary output voltage and the second reference voltage is fed back tothe triggering controller 606, which can be a PWM controller in thisembodiment. When the auxiliary output voltage is lower than the secondreference voltage, the comparator outputs a high-level signal todecrease switching frequency of the first control signal S1 and thefourth control signal S4. Where the first control signal S1 and thefourth control signal S4 are a driving signal for a gate-source voltageVgs of the first semiconductor component 601 and that of the fourthsemiconductor component 604, respectively. In addition, the auxiliaryoutput voltage would reduce when the DC-to-DC conversion apparatus 60operates at a heavy-load condition. Thus, during the negative half cycleof the quasi-sinusoidal current, the comparator outputs a high-levelsignal to decrease switching frequency of the second control signal S2and the third control signal S3, thus increasing the auxiliary outputvoltage and stabilizing it at +6V. Where the second control signal S2and the third control signal S3 are a driving signal for a gate-sourcevoltage Vgs of the second semiconductor component 602 and that of thethird semiconductor component 603, respectively. In addition, becausethe auxiliary output voltage is proportional to the main output voltage(in this example, the main output voltage is twice of the auxiliaryoutput voltage), the main output voltage can be stabilized at +12V.

However, the above-mentioned examples of providing a voltage-stabilizingfunction are for demonstration and not for limitation of the presentinvention. Furthermore, the voltage-stabilizing circuits depend on thedeveloped topologies of the switching power supply.

Therefore, the control signals for gate-source voltages of thecontrollable semiconductor components, which are MOSFETs in thisembodiment, are controlled by sensing the main output voltage or theauxiliary output voltage. In addition, in this embodiment, the firstsemiconductor component 601 and the second semiconductor component 602can be the uncontrollable semiconductor components, such as diodes. Moreparticularly, the third semiconductor component 603 and the fourthsemiconductor component 604 must be the controllable semiconductorcomponents, such as MOSFETs, BJTs, or IGBTs. In other words, all of thefour semiconductor components 601-604 are the controllable semiconductorcomponents; or the first semiconductor component 601 and the secondsemiconductor component 602 are the uncontrollable semiconductorcomponents, whereas the third semiconductor component 603 and the fourthsemiconductor component 604 are the controllable semiconductorcomponents.

Reference is made to FIG. 4A which is a circuit diagram of a secondembodiment of a multi-output DC-to-DC conversion apparatus with avoltage-stabilizing function. The multi-output DC-to-DC conversionapparatus 60 generates at least two output voltages, namely, a mainoutput voltage and an auxiliary output voltage. The auxiliary outputvoltage is lower than the main output voltage and is functioned as aninput voltage of a buck converter, and the buck converter is provided toconvert the auxiliary output voltage into at least one lower adjustableDC voltage. The multi-output DC-to-DC conversion apparatus 60 includes amain transformer 500, a semiconductor component group 600, and atriggering controller 606.

The main transformer 500 has a primary winding (not labeled), a firstsecondary winding (not labeled), and a second secondary winding (notlabeled). The primary winding has a dotted terminal (not labeled) and anon-dotted terminal (not labeled). The first secondary winding and thesecond secondary winding have a center tap, a dotted terminal (notlabeled), a non-dotted terminal (not labeled), and a medium terminal(not labeled), respectively.

The semiconductor component group 600 is electrically connected betweenthe dotted terminal and the non-dotted terminal of the main transformer500. One output terminal of the semiconductor component group 600 is theground (not labeled) and the other output terminal is an auxiliaryoutput terminal Vo2, and the auxiliary output terminal Vo2 provides theauxiliary output voltage to the ground. The medium terminal of the firstsecondary winding is a main output terminal Vo1, which provides the mainoutput voltage to the ground.

The semiconductor component group 600 is composed of four semiconductorcomponents, which have a first semiconductor component 601, a secondsemiconductor component 602, a third semiconductor component 603, and afourth semiconductor component 604, respectively. Each of the foursemiconductor components 601-604 has at least one first terminal (notlabeled) and a second terminal (not labeled). As shown in FIG. 4A, thedotted terminal of the first secondary winding of the main transformer500 is electrically connected to the first terminal of the secondsemiconductor component 602, and the non-dotted terminal of the firstsecondary winding is electrically connected to the first terminal of thefirst semiconductor component 601. Also, the non-dotted terminal of thesecond secondary winding is electrically connected to the first terminalof the third semiconductor component 603.

All of the four semiconductor components 601-604 are controllablesemiconductor components, such as MOSFETs, BJTs, or IGBTs. In thisexample, more particularly, the MOSFETs are exemplified for furtherdemonstration.

In addition, the second terminal of the first semiconductor component601 is electrically connected to the second terminal of the secondsemiconductor component 602 and the medium terminal of the secondsecondary to form the auxiliary output terminal Vo2. Also, the secondterminal of the third semiconductor component 603 is electricallyconnected to the second terminal of the fourth semiconductor component604 to from the ground.

The triggering controller 606 is electrically connected to the mainoutput terminal Vo1 and the auxiliary output terminal Vo2 to generate aplurality of control signals S1-S4. The duty cycle of the semiconductorcomponent group 600 is controlled by the control signals S1-S4 tostabilize the main output voltage and the auxiliary output voltage. Thedetailed operation of the triggering controller 606 will be madehereinafter.

Reference is made to FIG. 4B which is a circuit diagram of the secondembodiment that the multi-output DC-to-DC conversion apparatus isoperated with current in a positive half-cycle. The main transformer 500receives a processed primary-side current from the front-end circuit,and the primary-side current is a quasi-sinusoidal current. Thus, theprimary-side current hereinafter is referred to as the quasi-sinusoidalcurrent. During the positive half cycle of the quasi-sinusoidal current,the quasi-sinusoidal current flows out the non-dotted terminal of theprimary winding; and a secondary-side current flows into the non-dottedterminal of the first secondary winding and the second secondarywinding, respectively. In this condition, the first semiconductorcomponent 601 and the third semiconductor component 603 of thesemiconductor component group 600 are forward biased, whereas the secondsemiconductor component 602 and the fourth semiconductor component 604are reverse biased. Hence, the first semiconductor component 601 and thethird semiconductor component 603 are turned-on; the secondsemiconductor component 602 and the fourth semiconductor component 604are turned-off. The direction of arrow, shown in FIG. 4B, represents thedirection of current flowing in the main transformer 500 and thesemiconductor component group 600. Besides, the DC-to-DC conversionapparatus 60 further have inductor-capacitor filters (not labeled),which are used to filter the main output voltage and the auxiliaryoutput voltage.

Reference is made to FIG. 4C which is a circuit diagram of the secondembodiment that the multi-output DC-to-DC conversion apparatus isoperated with current in a negative half-cycle. During the negative halfcycle of the quasi-sinusoidal current, the quasi-sinusoidal currentflows out the dotted terminal of the primary winding; and thesecondary-side current flows into the dotted terminal of the firstsecondary winding and the second secondary, respectively. In thiscondition, the second semiconductor component 602 and the fourthsemiconductor component 604 of the semiconductor component group 600 areforward biased, whereas the first semiconductor component 601 and thethird semiconductor component 603 are reverse biased. Hence, the secondsemiconductor component 602 and the fourth semiconductor component 604are turned-on; the first semiconductor component 601 and the thirdsemiconductor component 603 are turned-off. The direction of arrow,shown in FIG. 4C, represents the direction of current flowing in themain transformer 500 and the semiconductor component group 600. Besides,the DC-to-DC conversion apparatus 60 further have inductor-capacitorfilters (not labeled), which are used to filter the main output voltageand the auxiliary output voltage.

Accordingly, the center-tapped main transformer 500 with the dualsecondary winding is applied to provide two output voltages from theDC-to-DC conversion apparatus 60:

1. The main output voltage is generated from connecting the mediumterminal of the first secondary winding and that of the second secondarywinding in series;

2. The auxiliary output voltage is generated from the medium terminal ofthe second secondary winding.

However, the two-output DC-to-DC conversion apparatus 60 is example fordemonstration and not for limitation of the present invention.

Evidently, the main output voltage is twice of the auxiliary outputvoltage. More particularly, the main output voltage and the auxiliaryoutput voltage can be stabilized in the predetermined voltages by thevoltage-stabilizing feedback control.

In order to stabilize the main output voltage and the auxiliary outputvoltage in the predetermined voltages to supply the loads due to thevariation of the input voltage as well as the load variation. Thefollowing schemes can be employed:

A comparator (not shown) is used to compare the main output voltage witha first reference voltage (not shown). The first reference voltage is,namely, the expected main output voltage of the multi-output DC-to-DCconversion apparatus 60, and which is assumed as +12V. Moreparticularly, a voltage difference between the actual main outputvoltage and the first reference voltage is fed back to the triggeringcontroller 606, which can be a PWM controller in this embodiment. Whenthe main output voltage is higher than the first reference voltage, thecomparator outputs a low-level signal to increase switching frequency ofthe first control signal S1 and the third control signal S3 during thepositive half cycle of the quasi-sinusoidal current. Where the firstcontrol signal S1 and the third control signal S3 are a driving signalfor a gate-source voltage Vgs of the first semiconductor component 601and that of the third semiconductor component 603, respectively. Inaddition, the main output voltage would increase when the input voltageof the DC-to-DC conversion apparatus 60 increases. Thus, during thenegative half cycle of the quasi-sinusoidal current, the comparatoroutputs a low-level signal to increase switching frequency of the secondcontrol signal S2 and the fourth control signal S4, thus reducing themain output voltage and stabilizing it at +12V. Where the second controlsignal S2 and the fourth control signal S4 are a driving signal for agate-source voltage Vgs of the second semiconductor component 602 andthat of the fourth semiconductor component 604, respectively. Inaddition, because the auxiliary output voltage is proportional to themain output voltage (in this example, the main output voltage is twiceof the auxiliary output voltage), the auxiliary output voltage can bestabilized at +6V.

Similarly, a comparator (not shown) is used to compare the auxiliaryoutput voltage with a second reference voltage (not shown). The secondreference voltage is, namely, the expected auxiliary output voltage ofthe multi-output DC-to-DC conversion apparatus 60, and which is assumedas +6V. More particularly, a voltage difference between the actualauxiliary output voltage and the second reference voltage is fed back tothe triggering controller 606, which can be a PWM controller in thisembodiment. When the auxiliary output voltage is lower than the secondreference voltage, the comparator outputs a high-level signal todecrease switching frequency of the first control signal S1 and thethird control signal S3 during the positive half cycle of thequasi-sinusoidal current. Where the first control signal S1 and thethird control signal S3 are a driving signal for a gate-source voltageVgs of the first semiconductor component 601 and that of the thirdsemiconductor component 603, respectively. In addition, the auxiliaryoutput voltage would increase when the input voltage of the DC-to-DCconversion apparatus 60 decreases. Thus, during the negative half cycleof the quasi-sinusoidal current, the comparator outputs a high-levelsignal to decrease switching frequency of the second control signal S2and the fourth control signal S4, thus increasing auxiliary outputvoltage and stabilizing it at +6V. Where the second control signal S2and the fourth control signal S4 are a driving signal for a gate-sourcevoltage Vgs of the second semiconductor component 602 and that of thefourth semiconductor component 604, respectively. In addition, becausethe auxiliary output voltage is proportional to the main output voltage(in this example, the main output voltage is twice of the auxiliaryoutput voltage), the main output voltage can be stabilized at +12V.

However, the above-mentioned examples of providing a voltage-stabilizingfunction are for demonstration and not for limitation of the presentinvention. Furthermore, the voltage-stabilizing circuits depend on thedeveloped topologies of the switching power supply.

Therefore, the control signals for gate-source voltages of thecontrollable semiconductor components, which are MOSFETs in thisembodiment, are controlled by sensing the main output voltage or theauxiliary output voltage. In addition, in this embodiment, the firstsemiconductor component 601 and the second semiconductor component 602can be the uncontrollable semiconductor components, such as diodes. Moreparticularly, the third semiconductor component 603 and the fourthsemiconductor component 604 must be the controllable semiconductorcomponents, such as MOSFETs, BJTs, or IGBTs. In other words, all of thefour semiconductor components 601-604 are the controllable semiconductorcomponents; or the first semiconductor component 601 and the secondsemiconductor component 602 are the uncontrollable semiconductorcomponents, whereas the third semiconductor component 603 and the fourthsemiconductor component 604 are the controllable semiconductorcomponents.

The auxiliary output voltage is functioned as an input voltage of thebuck converter 70, and the buck converter 70 converts the auxiliaryoutput voltage into lower adjustable DC voltages, such as a first outputvoltage Vb1 and a second output voltage Vb2 (as shown in FIG. 2). Hence,the first output voltage Vb1 and the second output voltage Vb2 can be,but not limited to, a 5-volt DC voltage and a 3.3-volt DC voltage,respectively. In this example, the lower-level voltage (+6V) isfunctioned as the input voltage of the buck converter 70, but not thehigher-level voltage (+12V). Thus, the lower-level auxiliary outputvoltage (+6V) is near the output voltage (+5V/+3.3V) of the buckconverter 70, this can increase efficiency of the buck converter 70.

In conclusion, the present invention has following advantages:

1. The triggering controller 606 can generate a plurality of controlsignals to turn on and turn off the semiconductor component group 600during the positive and negative half cycle of the quasi-sinusoidalcurrent. Therefore, the main output voltage and the auxiliary outputvoltage are stabilized in the predetermined voltages according to thevoltage difference between the actual main output voltage and theexpected output voltage and the voltage difference between the actualauxiliary output voltage and the expected output voltage.

2. The DC-to-DC conversion apparatus 60 generates a lower-levelauxiliary output voltage (with respective to the main output voltage),which is functioned as an input voltage of the buck converter 70.Because the lower-level auxiliary output voltage is near the outputvoltage of the buck converter 70, this can result in increasedefficiency of the buck converter 70.

Although the present invention has been described with reference to thepreferred embodiment thereof, it will be understood that the inventionis not limited to the details thereof. Various substitutions andmodifications have been suggested in the foregoing description, andothers will occur to those of ordinary skill in the art. Therefore, allsuch substitutions and modifications are intended to be embraced withinthe scope of the invention as defined in the appended claims.

1. A multi-output DC-to-DC conversion apparatus with avoltage-stabilizing function generating at least a main output voltageand an auxiliary output voltage; the auxiliary output voltage beinglower than the main output voltage and functioned as an input voltage ofa buck converter, and the buck converter being provided to convert theauxiliary output voltage into at least one lower adjustable DC voltage;the multi-output DC-to-DC conversion apparatus comprising: a maintransformer having a primary winding and a secondary winding; whereinthe secondary winding has a dotted terminal, a non-dotted terminal, anda medium terminal; a semiconductor component group electricallyconnected to the dotted terminal and the non-dotted terminal of thesecondary winding of the main transformer; wherein one output terminalof the semiconductor component group is the ground, and the other outputterminal is a main output terminal, which provides the main outputvoltage to the ground; the medium terminal is an auxiliary outputterminal, which provides the auxiliary output voltage to the ground; anda triggering controller electrically connected to the main outputterminal and the auxiliary output terminal and generating a plurality ofcontrol signals to control switching frequency of the semiconductorcomponent group for stabilizing the main output voltage and theauxiliary output voltage; whereby a center-tapped of the maintransformer with the secondary winding provides a lower-level voltage,which is functioned as the input voltage of the buck converter toincrease efficiency of the buck converter.
 2. The multi-output DC-to-DCconversion apparatus in claim 1, wherein the semiconductor componentgroup includes at least four semiconductor components.
 3. Themulti-output DC-to-DC conversion apparatus in claim 1, wherein the mainoutput voltage is twice of the auxiliary output voltage.
 4. Themulti-output DC-to-DC conversion apparatus in claim 1, wherein thetriggering controller is a pulse-width modulation controller.
 5. Themulti-output DC-to-DC conversion apparatus in claim 2, wherein thesemiconductor components are controllable semiconductor components. 6.The multi-output DC-to-DC conversion apparatus in claim 2, wherein thesemiconductor components are partially uncontrollable semiconductorcomponents.
 7. The multi-output DC-to-DC conversion apparatus in claim1, wherein the switching frequency of the control signals outputted fromthe triggering controller is controlled by comparing the main outputvoltage with a predetermined voltage by the triggering controller. 8.The multi-output DC-to-DC conversion apparatus in claim 1, wherein theswitching frequency of the control signals outputted from the triggeringcontroller is controlled by comparing the auxiliary output voltage witha predetermined voltage by the triggering controller.
 9. Themulti-output DC-to-DC conversion apparatus in claim 1, furthercomprising inductor-capacitor filters to filter the main output voltageand the auxiliary output voltage.